Tyrosine phosphorylation of proteins plays an important role in cellular signaling and many cellular activities. The levels of cellular phosphorylation are reversibly controlled by protein tyrosine kinases and protein tyrosine phosphatases. The murine R-PTP-κ, a receptor-type protein tyrosine phosphatase, has recently been cloned. In order to identify the protein tyrosine phosphatases critical to the cellular signal transduction in human keratinocytes, a polymerase chain reaction (PCR)-based strategy was employed, and we have cloned a human homologue of the murine R-PTP-κ. Here, we report the isolation of a complementary DNA encoding a human R-PTP-κ. of the several overlapping cDNA clones, one clone, which we originally termed p55-7, was found to encode a transmembrane protein of 1440 amino acids and was highly conserved with murine R-PTP-κ with 98% identity at the amino-acid levels. The human R-PTP-κ gene was localized to chromosome 6 by southern hybridization of DNA from a rodent/human somatic cell mapping panel. Northern blot analysis of RNA from several human tissues revealed, like the murine R-PTP-κ, the presence of a major mRNA of approx. 7.0 kb and a minor mRNA of approx. 5.3 kb. In contrast to the expression of murine R-PTP-κ which was highly expressed in liver and kidney, the human R-PTP-κ was predominantly expressed in spleen, prostate, and ovary. However, the transcripts were detectable at various levels in all examined tissues (thymus, testis, small intestine, and colon) except for PBL (peripheral blood leukocytes). In addition, human R-PTP-κ displayed a restricted pattern of expression among a series of cell lines, and was apparently expressed in an epidermal cells and cell lines (human normal keratinocytes, HaCaT, and A431), but was not detectable in other cell lines tested after longer exposure.